1. Field of the Invention.
The subject invention relates to an improved seal between an elongate convex metallic nipple and a concave recessed metallic seal surface, such as in a cylinder valve connection.
2. Description of the Prior Art.
Many chemical processes require the presence of a specified gas. Examples of gases required in various chemical processes are: arsine, carbon monoxide, deuterium, deuterium selenide, diborane, 1,1-difluoroethylene, ethane, ethylene, germane, hydrogen, hydrogen selenide, methane, methyl fluoride, natural gas, pentaborane, phosphine, silane, stibine, tetrafluoroethylene, vinyl fluoride. The selection of a particular gas and the assurance of purity of the gas are very important. Gases typically are stored under high pressure in metallic containers. The most common such containers are referred to as gas cylinders, which typically are considered to include metallic containers that are dimensioned to hold up to 1,000 pounds of water. Larger containers typically are referred to in the industry as ton containers. Still larger containers used for transporting gas are referred to in the industry as tube trailers.
Gases can be produced with a very high degree of purity. However, impurities can become a significant factor during the initial filling of the metallic container and subsequently as the gas flows from the metallic container and toward its intended point of use. Impurities also can be a factor when the container is prepared under heat and vacuum prior to filling.
The prior art gas container typically has a valve which can be selectively opened or closed to permit the filling of the cylinder and to subsequently permit the use of the gas. The typical prior art valve for a gas container includes a generally tubular metallic outlet with an array of threads and an internal bore which communicates with the valving element and with the interior of the gas container. The bore of the prior art valve outlet typically includes a large diameter cylindrical entry, a recessed conically tapered metallic seal surface and a smaller diameter cylindrical channel leading from the tapered outlet seat toward the valving element and the interior of the gas container.
The prior art valve outlet of a gas container is used with a prior art nipple. The nipple is an elongate generally tubular metallic member having opposed ends and a gas passage extending axially therethrough. One end of the prior art nipple includes a cylindrical neck having a diameter less than the diameter of the enlarged cylindrical entry to the bore of the valve outlet. The cylindrical neck terminates at a convexly arcuate mating end which is dimensioned to engage the conically tapered seat of the valve outlet to define an annular region of metal-to-metal mating contact.
The prior art nipple further includes a shoulder adjacent the cylindrical neck of the nipple and a shank which extends from the shoulder toward the opposed end of the nipple. The shank defines a diameter less than the diameter of the shoulder. Thus, a radially aligned step is defined between the shoulder and the shank.
The prior art valve outlet connection further includes a nut having an array of threads that can be mated with the threads on the valve outlet. The prior art nut further includes an inwardly extending flange defining an opening that is greater than the diameter of the shank on the nipple but smaller than the diameter of the shoulder on the nipple. Thus, the inwardly extending flange on the nut will engage against the step on the shoulder of the prior art nipple. The flange of the nut will exert axial forces on the shoulder of the nipple as the nut is threadedly engaged with the valve outlet. These axially forces are intended to urge the arcuately convex mating end of the nipple into sealing engagement with the conically tapered seat in the bore of the valve outlet.
The above described prior art connection generally works well. However, the nose of the prior art nipple and/or the tapered seat of the prior art bore can become galled after several mating and unmating operations. Discontinuities in either of the two mating surfaces can affect the quality of the seal. An imperfect seal may permit gas that had been stored in the container to escape and/or can permit ambient air to contaminate the gas being filled into the container delivered from the container to a specified chemical process. Impurities in the gas used in many industries, such as the semi-conductor industry, can significantly affect the quality of the product being produced. Additionally, galling, scratches or other surface discontinuities become worse over time and can spread from one component to another. Thus, for example, a surface discontinuity on one nipple can cause a similar surface discontinuity on a valve outlet mated therewith. After the gas in the cylinder has been depleted, the cylinder with the damaged valve outlet will be refilled and may be used with another nipple. The surface discontinuity that had been imposed upon the tapered seat of the valve outlet will then create a new surface discontinuity in the next nipple mated therewith.
Fittings employed in other environments frequently use gaskets, washers or seals to prevent damage or to minimize the effects of damage. Many such prior art fittings employ gaskets, washers or seals formed from an elastomeric material. The elastomer will deform during mating and will fill any surface discontinuities that may exist. Elastomers, however, generally are unacceptable for most high purity gas delivery systems. In particular, particles of the elastomeric material can contaminate the otherwise highly pure gas. Furthermore, some gases can leak through a thin polymer gasket. As a result, elastomeric gaskets typically are not used in systems for delivering high purity gases.
Annular metallic gaskets with opposed parallel planar faces often are used in high purity gas delivery systems. The planar faces of these prior art gaskets generally are placed between opposed planar mating faces of a fitting. Prior art gaskets of this general type are not suitable for the above described gas containers in view of the recessed portion of the outlet and the elongate nose of the nipple which results in an inaccessible seal region.
The prior art also includes shallow dished washers to fit between mating convex and concave surfaces of a fitting. Shallow dished washers are shown, for example, in U.S. Pat. No. 1,649,673 to Dyck, U.S. Pat. No. 3,797,835 to Wehner, U.S. Pat. No. 4,540,205 to Watanabe et al. and U.S. Pat. No. 4,570,981 to Fournier et al. Shallow dished washers have been used in the prior art primarily to seal joints where the convex member is axially very short. Even in these situations, mounting of the dished washer has been difficult. For example, U.S. Pat. No. 3,797,835 to Wehner shows a complexly formed washer with clearly distinct angularly aligned surfaces for closely engaging comparable surfaces to be sealed. U.S. Pat. No. 4,540,205 to Watanabe et al. shows a tapered surface with an axially aligned annular groove and a dished washer with an axially aligned cylindrical projection that can be engaged in the groove of the tapered surface for holding the washer during assembly. Both the tapered surface and the cylindrical portion of the dished washer must be precisely manufactured relative to one another, thereby preventing the use of conventional valve outlets and nipples and adding significantly to costs. U.S. Pat. No. 4,570,981 to Fournier et al. includes an elastomeric sealing ring at the inner circumferential portion of the gasket. The elastomeric member will assist in holding the prior art dished washer in position prior to and during assembly. As noted above, the use of elastomeric materials in proximity to highly pure flowing gases is unacceptable.
Axially short dished washers would be undesirable for use with the above described cylinder valves and nipples in that precise positioning of the axially short dished washer at the mating end of the nipple could not be assured. A significantly off-center seating of a dished washer could readily occur and could either impede the gas flow or contribute to leaks across the seal. A soft metallic coating over the nose of the nipple could provide a high quality seal during the first mating of the nipple and the valve outlet. However, the soft coating material on the nipple could be damaged by surface irregularities on the valve outlet, and such damage to a coating would contribute to leaks during subsequent connections of the nipple to the valve outlet.
Accordingly, it is an object of the subject invention to provide an enhanced seal between a cylinder valve outlet and a nipple.
It is a further object of the subject invention to provide a seal enhancer that can ensure a high quality seal between a valve outlet and a nipple, one or both of which may have surface damage.
Another object of the subject invention is to provide a seal enhancer that will prevent or minimize damage to both a valve outlet and a nipple.
Still a further object of the subject invention is to provide a seal enhancer than can be manufactured inexpensively and reliably.
Yet an additional object of the subject invention is to provide a seal enhancer that can be easily positioned and removed and that has a readily apparent visible presence.